Examples of a small portable device is e.g. a headset for wireless communication through an antenna with a mobile communication apparatus, such as a mobile telephone, a Bluetooth device, or any portable or stationary electronic device. A small portable device is, as indicated, characterized in that it is small and light. Therefore, it is preferred if the antenna used in such a device is small, light, and efficient. The small portable device may communicate using a communication protocol, such as the Bluetooth, the WLAN (Wireless Local Area Network), the UMTS (Universal Mobile Telecommunications System), or the GSM (Global System for Mobile communications) protocol.
One example of an antenna for a small portable device is a monopole antenna, which extends out of the product. Another solution is a PIFA (Planar Inverted F Antenna) antenna. However, there are several drawbacks of these antennas. To achieve sufficient bandwidth to meet the requirements of known communication protocols, e.g. according to above, the known antennas all need ground planes, which are too big to fit in a small portable device.
There are a number of problems with the known prior art-antennas, which make them unsuitable for use in a small portable device.
Firstly, the size of the small portable device causes problems for the antenna design, as it entails limited battery capacity. This means that the antenna should have a high efficiency in order not to waste battery power. Small antennas have lower efficiency than big antennas. As the device is small, the ground plane will also be small. An antenna requires a certain ground plane size to achieve a certain bandwidth, which is necessary for the antenna to be able to operate under a specific communications protocol, which always requires a certain bandwidth.
Secondly, since cost is often important for a small portable device it is important that the antenna can be made cheaply, which is not always the case with the antennas known in the art.
Thirdly, because of the small nature of the small portable device, other parts of the device will be very close to the antenna, which can have a negative influence on the antenna performance. Especially conducting materials like batteries, knobs or ESD (electrostatic discharge) means can have a very negative influence on the antenna performance. Therefore, the antenna has to work well in this environment, which is also not possible with the antennas according to the known prior art.